We have developed and characterized the only myelogenous leukemia cell line (K-562) available, originally derived from patient with CML. The K-562 cell line has the Philadelphia (Ph1 plus) chromosome and Fc receptor after 6 1/2 years in culture. It is free of Epstein-Barr virus genome, herpes-like virus and mycoplasma, reverse transcriptase, and does not have T or B cell markers. These K-562 cells, when injected into rabbits or a monkey, elicit the production of specific antibody which demonstrates complement mediated cytotoxicity for the leukocytes of patients with leukemia. Specificity for the myelogenous leukemia cells is obtained after absorption of antisera with normal peripheral leukocytes and bone marrow cells as well as with leukemia cells of other types (e.g., AML, ALL, CLL). A single polypeptide (77,000-80,000 daltons) has been isolated and characterized from the K-562 cells that specifically inhibits the cytotoxicity assay. Monospecific antiserum to this polypeptide is being prepared. The purpose of this project is: 1) to further characterize the K-562 cell antigen biochemically; 2) to isolate antigen(s) from leukemic cells of patients with AML, CML, ALL and CLL and to compare them biochemically and antigenically; 3) to assess the presence of antibody, antigen, or complexes in the sera of patients with leukemia using the isolated antigens and monospecific antisera; 4) to use the immunologic reagents (monospecific sera and characterized antigens) as reference standards to accurately detect incomplete remission and early relapses in patients with leukemia.